Normally, two different polymers because of the very low entropy of mixing. Sometimes, however, two different polymers can form a compatible blend with the aid of an agent. The agent can be a block copolymer of two homopolymers. One of the problems associated with the prior art agents and methods of blending is that it is not a simple task to find such an agent, to devise a commercially viable synthetic method for its preparation and to subsequently blend the components into an homogeneous material without macrophase separation. In many instances, polymer blends have useful properties which are either superior or not possessed by the constituent homopolymers. For example, many members of the family of premium materials called engineering resins, are compatibilized polymer blends.
Different polyolefins assembled from the same monomer molecules having different geometrical, chemical, or stereochemical isomeric structures are generally immiscible. A well known example is low density polyethylene manufactured at high pressure and high density polyethylene manufactured at low pressure. Other prior art examples include the products of Ziegler-Natta catalyzed propylene polymerization which include high molecular weight isotactic-crystalline polypropylene and low molecular weight amorphous polypropylene. The two polymers are immiscible and the amorphous polymer must be removed or its presence renders the crystalline polymer physically and mechanically too weak to be of any commercial value.
Well-defined organometallic compounds, such as Group IVB elements, of the Periodic Table (Handbook of Chemistry and Physics, 49th Edition, Ed. R. C. Weast, Chemical Rubber Co. Cleveland, 1968) have been found to possess stereoselectivity in the polymerization of propylene, styrene, and other .alpha.-olefins depending upon the ligand structure of the organometallic precursor.
For example, in one prior art method, chiral group IVB metallocene precursors act as catalysts for the isospecific polymerization of propylene to yield isotactic polypropylene, (See U.S. Pat. No. 4,794,096 and the articles by Kaminsky et al. Angew. Chem. Int. Ed. Engl. 1985,24, 307 and by Ewen in J. Am. Chem. Soc. 1984, 106, 6355).
In addition, Ewen et al. as disclosed in J. Am. Chem. Soc. 1988, 110, 6255 and U.S. Pat. No. 4,892,851 taught that zirconocene precursors having bilateral symmetry could produce syndiotactic polypropylene and are capable of polymerizing ethylene, .alpha.-olefins and cycloolefins with comparable activity.
Organometallic compounds having C.sub.2v symmetry, whether as a stereorigid zirconocene or a free rotating complex as disclosed by Chien et al., Macromolecules 1995, 28, 5399, tend to catalyze propylene polymerization without profacial selectivity. Similar nonspecific polymerizations of propylene have previously been catalyzed by titanium complexes with either a single .eta..sup.5 ligand or a phenolic ligand.
In the case of styrene, syndioselective polymerizations have been achieved using either mono .eta..sup.5 -ligands as disclosed by Ishihara et al in Macromolecules 1986, 19, 2464, or 2,2'-thiobis(6-t-butyl-4-methylphenoxy) ligands as disclosed by Miytake et al. in Makromol Chem. Macromol. Symp. 1993, 66, 203. Other prior methods have included the use of zirconocene dichloride and hafnocene dichloride as catalysts in the production of atactic polystyrenes.
All the above precursors and other conventional precursors have been used to provide for the linear polymerization of ethylene.
Brookhart et al. disclosed in J. Am. Chem. Soc. 1995, 117, 6414 that during the polymerization of ethylene in the presence of a 1.4-diaza-1,3-butadien-2-y nickel complex and a cocatalyst, branched polyethylene are produced.
All of the above precursor are activated by a cocatalyst which transforms the former catalist into the corresponding cationic species (See U.S. Pat. No. 5,198,401 and EP 573,403). The cocatalyst comprises a cation which irreversibly reacts with at least one ligand from either the Group IVB or VIIIB metal complexes to form the catalytically active cationic Group IVB or VIIIB complex. The counter anion is non-coordinating, readily displaced by a monomer or solvent, has a negative charge delocalized over the framework on the anion or within the core thereof, is not a reducing or oxidizing agent, forms stable salts with reducible Lewis acids and protonated Lewis bases, and is a poor nucleophile.
Other prior types of cocatalyst include Lewis acids which will irreversibly react with at least one ligand from a Group IVB metal complex to form an anion possessing many but not all of the characteristics described above (See Marks et al. J. Am. Chem. Soc. 1991, 113, 3623).
High molecular weight polypropylene having a certain steric structure, prepared individually in the presence of one of the prior art catalysts described above, is generally immiscible with another polypropylene of a different steric structure. For example, a solvent-casted blend of any pair of stereoisomeric polypropylenes, e.g., isotactic and atactic, etc., tend to crumble easily and the tensile bar press molded from the blend fails with the least bit of strain. Likewise linear polyethylenes and branched polyethylenes are immiscible as are mixtures of linear polypropylene and branched polypropylenes. Syndiotactic polystyrenes are typically incompatible with atactic polystyrenes.
In another prior process, solutions of two different metallocenes are used to polymerize monomers separately as if each is unaffected by the presence of the other. This method is useful for preparing polyethylenes with bimodal molecular weight distribution using two group IVB metallocenes as disclosed by Ewen, Studies in Surface Science and Catalysis Vol 25 Catalytic Polymerization of Olefins Eds. Keii et al., Kodansha, Elsevier, 1986, pp.271, and by Ahlers and Kaminsky, Makromol. Chem.; Rapid Commun. 1988,9, 457. A polypropylene having multimodal molecular weight distribution was obtained using an ansa-hafliocene and ansa-zirconocene mixture to produce isotactic polypropylenes albeit having molar masses that are different.
Despite all of the prior processes for preparing various polymers, there are no processes that are capable of forming compatibilized polyolefin blends of the present invention.
Unlike the prior art, the present invention allows one to synthesize, directly in a "one-pot" polymerization of a single monomer, useful blends of polyolefins having different steric structures and/or geometric structures without the need for subsequent blending of the polyolefins.
Thus, one object of the invention is to provide an olefin polymerization catalyst which can give olefin polymers of different structures A.sub.n and B.sub.m as well as a third substance having blocks of the same structures (A.sub.n.sup.1 B.sub.m.sup.2).sub.x in its chain, the latter is capable of bridging A.sub.n and B.sub.m thus compatibilizing the two isomeric homopolymers. For example, in one preferred embodiment, A.sub.n, is an isotactic polypropylene and B.sub.m is an atactic polypropylene having the microstructures shown in the following conventional projection: ##STR1##
The subscripts .sup.n and .sup.m indicate that the number of monomeric units in the homopolymers which are large integers (10 to 30,000); the subscripts.sub.n.sup.1 and.sub.m.sup.1 indicate the number of monomeric units in the block copolymers which are smaller integers (10 to 1,000), and x ranging from 10 to 100 denotes the number of AB blocks.
Another object of this invention is to provide a catalyst composition for the "one-pot" direct synthesis of materials as disclosed in projection 1 wherein A.sub.n and B.sub.m can also be syndiotactic polypropylene, and hemiisotactic polypropylene. For any combination, A.sub.n and B.sub.m will always have different microstructures.
Another object of this invention is to provide a catalyst composition for the "one-pot" direct synthesis of the materials of projection 1 wherein A.sub.n is linear polyethylene and B.sub.m is branched polyethylene.
Another object of this invention is to provide a catalyst composition for the "one-pot" direct synthesis of materials of projection 1 wherein A.sub.n is ethylene- .alpha.-olefin copolymer (commonly referred to as liner low density polyethylene) and B.sub.m is a linear ethylene homopolymer (polyethylene).
Another object of this invention is to provide novel polymer blends from two different monomers.
Another object of this invention is to provide a catalyst composition for the "one-pot" direct synthesis of materials as shown in projection 1 wherein A.sub.n is a linear polypropylene having either an isotactic, syndiotactic or atactic microstructure and B.sub.m is a branched polypropylene.
Another object of this invention is to provide a catalyst composition for the "one pot" direct synthesis of the materials of projection 1 wherein A.sub.n is syndiotactic polystyrene and B.sub.m is atactic polystyrene.
Another object of this invention is to provide novel polymer blends from a single monomer exhibiting properties of plastics with a wide range of stiffness, hardness, impact strength, and abrasion resistance.
Another object of this invention is to provide novel polymer blends from a single monomer exhibiting properties of elastomers with 0 range of modulus, elasticity and cross link density of physical nature.
Another object of this invention is to provide novel low molecular weight polyolefin mixtures from a single monomer exhibiting properties suited for lubricant and motor oil applications.
Another object of this invention is to provide novel materials from a single monomer exhibiting properties characteristic of a plastomer.
Another object of this invention is to provide novel polymer blends from a single monomer exhibiting properties characteristic of a flexomer.
Another object of this invention is to provide novel polymer blends from a single monomer exhibiting properties characteristic of a thermoplastic elastomer.
Another object of this invention is to provide novel polymer blends from a simple monomer exhibiting properties characteristic of an elastomer.
Another object of this invention is to provide novel blend exhibiting unusual properties and having the characteristics of a tough plastomer, thermoplastic elastomer, gum rubbers and lubricating fluid, wherein all these materials are processed like thermoplastics.
A name is lacking for the novel materials of the present invention. The properties of the material suggest the following terms: interfacial polymer blends, interpenetrating polymer blends, naturally compatibilized polymer blends, or simply compatible polymer blends. These terms are used herein interchangeably but do not exclude other more suitable names.